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| United States Patent |
6,198,381
|
|
Turner
, et al.
|
March 6, 2001
|
Delayed reset mode model for electronic identification systems
Abstract
There is disclosed and claimed an electronic identification system
including at east one reader and a plurality of transponders to be read by
the reader. Each transponder has a normal operational mode 32 wherein it,
in response to an interrogation signal from the reader transmits a code 36
to the reader, and a monitor mode 40 wherein it is still sensitive and
responsive to signals from the reader, but wherein it does not transmit
the code. The reader is adapted to cause a transponder of which the code
has been read, to switch from the normal operational mode to the monitor
mode, by transmitting a first signal S.sub.1 to the transponder. The
transponder, while being in the monitor mode, is sensitive to a second
signal S.sub.2 and responsive upon receipt of the second signal, to reset
to the normal operational mode.
| Inventors:
|
Turner; Christopher Gordon Gervase (Gauteng, ZA);
Kruger; Johan Dawid (Gauteng, ZA)
|
| Assignee:
|
Data Investments Limited (Tortola, VG)
|
| Appl. No.:
|
160354 |
| Filed:
|
September 25, 1998 |
Foreign Application Priority Data
| Current U.S. Class: |
340/10.1; 340/10.3; 340/572.1 |
| Intern'l Class: |
H04Q 005/22 |
| Field of Search: |
340/825.54,825.49,825.31,825.34,572.1,10.1,10.3
342/42,44
|
References Cited
U.S. Patent Documents
| 5189246 | Feb., 1993 | Marsh et al.
| |
| 5282421 | Feb., 1994 | Marsh et al.
| |
| 5353009 | Oct., 1994 | Marsh et al.
| |
| 5406890 | Apr., 1995 | Marsh et al.
| |
| 5519381 | May., 1996 | Marsh et al.
| |
| 5537105 | Jul., 1996 | Marsh et al.
| |
| 5557280 | Sep., 1996 | Marsh et al.
| |
| 5566441 | Oct., 1996 | Marsh et al.
| |
| 5699066 | Dec., 1997 | Marsh et al.
| |
| 5726630 | Mar., 1998 | Marsh et al.
| |
| Foreign Patent Documents |
| 0 467 036 A2 | Jan., 1992 | EP.
| |
| 0 494 114 | Jul., 1992 | EP.
| |
Other References
U.S. Ser. No. 09/138,560 filed on Aug. 24, 1998.
U.S. Ser. No. 09/143,711 filed on Aug. 28, 1998.
|
Primary Examiner: Tokar; Michael
Assistant Examiner: Jeanglaude; Jean B.
Attorney, Agent or Firm: Finnegan, Henderson, Farabow, Garrett & Dunner, L.L.P.
Claims
What is claimed is:
1. An electronic identification system including:
at least one reader;
a plurality of transponders to be read by the at least one reader, each
transponder having a first mode for transmitting a code to the at least
one reader in response to an interrogation signal from said at least one
reader, and a second mode wherein the transponder is sensitive and
responsive to signals from said at least one reader, but does not transmit
the code;
said at least one reader in use being operative immediately after reading
the code of any one transponder, to transmit a first signal causing that
one transponder to switch from said first mode to the second mode; and
the one transponder remaining in the second mode, whether the one
transponder is energized or not, until a reset signal is received by the
one transponder from the reader.
2. A system as claimed in claim 1 wherein the transponder automatically
resets to the first mode after remaining in the second mode for a
predetermined time period, if by then the reset signal has not yet been
received from the reader.
3. A transponder for use in an electronic identification system including
at least one reader and a plurality of transponders to be read by the at
least one reader, the transponder including:
a controller having a first mode for causing a code to be transmitted by
the transponder to the at least one reader in response to an interrogation
signal from said at least one reader; and a second mode wherein the
controller is still sensitive and responsive to signals from said at least
one reader, but does not cause the transponder to transmit the code;
the controller being responsive to a first signal from said at least one
reader by switching from said first mode to said second mode; and
the controller remaining in said second mode, whether the transponder is
energized or not, until a reset signal is received by the controller from
said at least one reader.
4. A transponder as claimed in claim 3 wherein the controller automatically
resets to the first mode after remaining in the second mode for a
predetermined time period, if by then the reset signal has not yet been
received by the transponder.
5. A method of operating an electronic identification system including at
least one reader and a plurality of transponders, the method including the
steps of:
transmitting an interrogation signal from the at least one reader to the
transponders in a first transponder mode,
receiving a response signal from a transponder and reading a code carried
by the response signal at the reader;
immediately after reading the code of any one transponder, transmitting a
first signal to said transponder to cause the transponder to switch from
said first mode to a second mode wherein the transponder is sensitive and
responsive to signals from the reader, but does not transmit the code;
causing the transponder to remain in the second mode, whether the
transponder is energized or not, until a reset signal is received by the
transponder from the reader, and transmitting to said transponder the
reset signal to cause the transponder to switch from said second mode to
said first mode.
6. A method as claimed in claim 5 including the step of causing the
transponder to remain in the second mode for a predetermined time period
after which the transponder is caused automatically to switch to the first
mode, if the reset signal has not been received by then.
Description
INTRODUCTION AND BACKGROUND
THIS invention relates to radio frequency (RF) electronic identification
systems comprising an interrogator and a plurality of transponders. The
invention more particularly relates-to operational modes for transponders
forming part of such a system.
A known system of the aforementioned kind includes a reader comprising a
transmitter for transmitting an RF energizing signal to the transponders
and a receiver for receiving a response signal from the transponders. A
microprocessor in the reader identifies a particular transponder by
identification code data modulated on the response signal by the
transponder when in a normal operational mode. Upon receipt of the data by
the reader and thus upon identification of the transponder, the reader
transmits a first signal to the transponder to switch it to a catnap mode
wherein it no longer is responsive and thus stops responding to the
interrogation signal, even while still being energized. After energization
of the transponder has been removed for a period longer than a short reset
period (typically shorter than 2 to 10 seconds) the transponder reverts to
the normal operational mode, wherein it will again respond with
identification code data upon being energized.
The aforementioned known transponders are also adapted to be switched from
the operational mode to a sleep mode upon receipt of a second signal from
the reader. When so switched, the transponders internal clock is stopped
and it remains in this mode wherein it is not responsive to any signal for
a period as long as an internal capacitor providing the transponder with
power, remains charged. It will be appreciated that this period is not of
a predictable length, but is dependent on the discharge rate of the
capacitor. which rate in turn is dependent on various other variables.
Other disadvantages of the mode of operation described hereinbefore and
which is charactefised by the rapid reset from the catnap mode to the
normal operational mode, are that scattering and reflections of the
interrogation signal may lead to multiple readings of a single
transponder; and that there is no method of controlling misreading of
transponders, so that transponder reading or interrogation has to be
performed under strictly controlled conditions. Furthermore, once the
transponder has switched to the aforementioned sleep mode, it cannot be
switched to the normal operational mode and it will only revert to the
normal operational mode after elapse of the aforementioned period.
OBJECT OF THE INVENTION
Accordingly, it is an object of the present invention to provide an
alternative electronic identification system, transponder and a method of
operating an identification system with which the applicant believes the
aforementioned disadvantages may at least be alleviated.
SUMMARY OF THE INVENTION
According to the invention there is provided an electronic identification
system including
at least one reader;
a plurality of transponders to be read by the at least one reader;
each transponder having a first or normal operational mode wherein it, in
response to an interrogation signal from said at least one reader,
transmits a code to the reader; and a second or monitor mode wherein it is
still sensitive and responsive to signals from said at least one reader,
but wherein it does not transmit the code;
said at least one reader being adapted to cause a transponder of which the
code is received, to switch from said first mode to the second mode by
transmitting a first signal to the transponder;
the transponder while being in the second mode being sensitive to a second
signal and responsive upon receipt of the second signal to reset to the
first mode.
In one embodiment of the invention the transponder, when in the second mode
and whether energized or not, remains in the second mode until the second
signal is received.
In another embodiment, the transponder may be arranged to remain in the
second mode for a predetermnined period, after which it automatically
resets to the first mode, if by then the second signal has not yet been
received by the transponder.
The invention also includes within its scope a transponder for use in an
electronic identification system including at least one reader and a
plurality of transponders to be read by the at least one reader, the
transponder including:
a controller having a first mode wherein it, in response to an
interrogation signal from said at least one reader, causes a code to be
transmitted to the reader, and a second mode wherein it is still sensitive
and responsive to signals from said at least one reader, but wherein it
does not cause the code to be transmitted;
the controller being responsive to a first signal from said reader by
switching from said first mode to said second mode; and
the controller also being responsive to a second signal from said at least
one reader by switching from said second mode to said first mode.
In one embodiment of the transponder, the controller when in the second
mode and whether the transponder is energized or not, remains in the
second mode until the second signal is received.
In another embodiment, the controller may be adapted to remain in the
second mode for a predetermined period after which it automatically resets
to the first mode, if by then the second signal has not yet been received
from said at least one reader.
The predetermined time period may be programmable and may be in the order
of 15 minutes to 30 minutes.
Also included within the scope of the present invention is a method of
operating an electronic identification system including at least one
reader and a plurality of transponders, the method including the steps of:
transmitting by means of said reader an interrogation signal to the
transponders which are in a first or normal operational mode;
receiving from a transponder a response signal;
transmitting a first signal to said transponder to cause the transponder to
switch from the first mode to a second or monitor mode
causing the transponder in the second mode still to be responsive to
signals from the reader, but to cease transmitting the response signal;
and
transmitting a second signal to said transponder to cause the transponder
to switch from said second mode to said first mode.
In one embodiment the method may include the step of causing the
transponder, when in the second mode and whether energized or not, to
remain in the second mode until the second signal is received.
In another embodiment, the method may include the steps of causing the
transponder to remain in the second mode for a predetermined time period
after which the is caused automatically to switch to the first mode, if
the second signal has not been received by then.
BRIEF DESCRIPTION OF THE ACCOMPANYING DIAGRAMS
The invention will now further be described, by way of example only, with
reference to the accompanying diagrams wherein:
FIG. 1 is a flow diagram of a mode model of a transponder forming part of a
prior art electronic identification system; and
FIG. 2 is a flow diagram of a mode model of a transponder according to the
invention forming part of an electronic identification system according to
the invention; and
FIG. 3 is a block diagram of an electronic identification system according
to the invention.
DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
A diagram illustrating the various modes and operation of a transponder
forming part of a prior art electronic identification system is generally
designated by the reference numeral 10 in FIG. 1.
The transponder has a normal operational mode 12 wherein it, when energized
at 14 by an interrogation signal from an interrogator or reader, by means
of backscatter modulation transmits at 16 an identification code to the
reader. The reader receives this signal and a microprocessor in the reader
identifies and if necessary, counts the transponder. The reader thereupon
transmits at 18 to the transponder a first signal S.sub.1 to cause the
transponder to cease transmitting the code and to enter a catnap mode at
20. The transponder remains in this mode until the end of a short period,
typically 2 to 10 seconds after the energization has been removed from the
transponder. After this short period has expired at 22, the transponder
thus rapidly resets to the normal operational mode wherein it can again be
read.
The transponder may also be switched to a sleep mode by transmitting a
second signal S.sub.2 from the reader, as shown at 24 in FIG. 1. In this
mode shown at 26, an internal clock of the transponder is stopped and the
transponder is incapable of any response to any signals from the reader.
The transponder remains in this mode for an indefinite period .tau., which
ends when an internal capacitor in the transponder is completely
discharged as shown at 28. This may take in the order of 30 seconds or
longer and only then does the transponder return to its normal operational
mode, wherein it can be read by a reader as hereinbefore described. The
discharge rate is dependent on various variables, which makes the length
of .tau. indefinite. The disadvantages of this prior art system and mode
model are set out in the introduction of this specification.
Referring to FIGS. 2 and 3, a mode model for a transponder 104.1 of an
electronic system 100; according to the invention is generally designated
by the reference numeral 30 in FIG. 2.
This model also comprises a first or normal operational mode 32 wherein the
transponder 104.1 is responsive to a reader 102 as hereinbefore described.
if the transponder is energized at 34 in FIG. 2 it causes an
identification code to be transmitted to the reader, as shown at 36. When
the reader receives the code, it transmits a first signal S.sub.1 to the
transponder. If the transponder receives this code at 38, its controller
106 switches to a second or monitor mode at 40 wherein it is still
sensitive and responsive to signals received from the reader, but wherein
it does not respond with the identification code.
Since the transponder, while in the monitor mode, is still sensitive to
signals from the reader, the controller 106 of the transponder 104.1 may
selectively be reset at any time to the operational mode, by transmitting
a second signal S.sub.2 to the transponder as shown at 46. In the
operational mode the transponder is again capable of being read by the
reader in that in this mode the transponder when energized, responds with
the identification code.
The prior art mode model may be referred to as a rapid reset mode model in
that the transponder automatically resets to the normal operational mode
after a short period .tau. after energization has been removed from the
transponder. The mode model according to the invention may be referred to
as a delayed reset mode model in that the transponder once read and in the
monitor mode (wherein it is still sensitive and responsive to signals from
the reader) can selectively be reset at any time to the normal operational
mode by transmitting the second signal. As an alternative, the transponder
may be arranged to remain in the monitor mode for a predetermined period
T, as shown at 42 in broken lines in FIG. 2, whereafter it automatically
resets to the normal operational mode as shown at 44, if by the end of the
period T, the second signal has not the been received. The period T may be
programmable and may be in the order of 15 minutes to 30 minutes. The
transponder, whether energized or not, remain in the monitor mode until
the second signal is received or until the end of the period T.
In use, the transponders must first be reset to the normal operational mode
by transmitting signal S.sub.2 as shown at 46. The transponders are now
ready to be read. During the reading step, the transponders are energized
as shown at 34. The codes are received and the transponders are
identified, recorded or counted, as the case may be and are switched to
the monitor mode as shown at 40. The monitor mode reduces the problem of
multiple readings due to scattering and reflections of the interrogation
signal. If required, the transponders can at any stage be reset to the
normal operational mode, by transmitting the signal S.sub.2.
The transponders according to the invention may be particularly useful in
electronic article surveillance (EAS) procedures. Such procedures are for
example utilized at an exit of a shop or the like to determine whether
transponders mounted on articles purchased have been read or whether some
articles and thus transponders have been shielded from readers at a point
of sale, either deliberately or incidentally. As explained hereinbefore,
the transponders read at the point of sale would all be in the monitor
mode 40. Only those transponders not read at the point of sale would still
be in the normal operational mode and could then be read and recorded by
the surveillance readers. The surveillance readers are adapted not to
transmit the first signal and thus to operate the shielded transponders in
loop A of the diagram in FIG. 2, to facilitate tracking and identification
of the associated articles.
It will be appreciated that there are many variations in detail on the
system, transponders and method according to the invention without
departing from the scope and spirit of the appended claims.
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